This application claims the priority of Korean Patent Application No. 10-2003-0055534 filed on Aug. 11, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
A system and a method consistent with the present invention relates to a domain name system, and more particularly, to a domain name service system and method thereof, wherein if a mobile host moves to an external link, a router connected to the mobile host transmits at least one address of at least one domain name server with the smallest hop count to the mobile host.
2. Description of the Related Art
A general mobile network system is divided into a home sub domain 10 and an external sub domain 20, depending on the locations of mobile hosts 11a and 21a. The mobile network system comprises first and second routers 40 and 50 connected to the home sub domain 10 and the external sub domain 20 via an Internet network 30, and first and second counterpart nodes 60 and 70 that are connected to the first and second routers 40 and 50, respectively, as shown in FIG. 1. Herein, it is assumed that the mobile hosts 11a and 21a are in communication with the first counterpart node 60.
The home sub domain 10 comprises a home link 11 including the mobile host 11a and a home agent 11b for managing the mobile host 11a; a domain name server 13 connected to the home link 11 via a sub network 12; and a gateway 14 connected to the sub network 12 for performing an Internet connection function.
The external sub domain 20 comprises an external link 21, including the mobile host 21a resulting from the movement of the mobile host 11a of the home sub domain 10, an external agent 21b for managing the mobile host 21a and a dynamic host configuration protocol (DHCP) server 21c for automatically configuring the address of the mobile host 21a; a domain name server 23 connected to the external link 21 via a sub network 22; and a gateway 24 connected to the sub network 22 for providing an Internet connection function.
Routers are used for the home agent 11b and the external agent 21b in the same manner as the first and second routers 40 and 50 that are connected to the counterpart nodes 60 and 70, respectively.
The operation of the mobile network system constructed as above will be described below.
In the mobile network system, if the mobile host 11a located at the home link 11 moves and is located at the external link 21, the mobile host 21a receives a message from the external agent 21b, which is different from that transmitted from the home agent 11b. Therefore, the mobile network system recognizes that the mobile host 21a is located at the external link 21 rather than the home link 11.
The mobile host 21a is allocated an address and network information through the DHCP server 21c or provided with a network prefix through the external agent 21b to create a care-of address by itself.
After the allocation of the address has been completed as described above, the mobile host 21a provides its changed address to the first counterpart node 60 and the home link 11 with which it was in communication when it was located at the home link 11. Through the provided address, the home agent 11b and the first counterpart node 60 store and manage the changed address therein.
Thereafter, the mobile host 21a can continuously communicate with the first counterpart node 60 based on the changed address.
The second counterpart node 70 which has not yet detected that the mobile host 21a has moved to the external link 21 sends a packet to the home agent 11b. The home agent 11b that has received the packet resends the packet to the mobile host 21a located at the external link 21 based on the stored address.
Therefore, the mobile host can continuously communicate without disconnection during and after its movement.
As for a domain name service, if the mobile host 11a of the home link 11 has moved to the external link 21, the mobile host 21a resulting from the movement uses a domain server address used in the domain name server 13 of the home sub domain 10.
Therefore, even when the mobile host 11a of the home link 11 has moved to the external link 21, the moved mobile host 21a still requests a domain name service through the domain name server 13 of the home link 11, as indicated by a dotted line 80 in FIG. 2.
However, this causes a problem in that there is a limitation on providing an efficient domain name service due to overload on network traffic since the mobile host 21a receives the domain name service through the domain name server 13 of the home link 11 even though the mobile host has moved from the home link 11 to the external link 21.